Carcinoembryonic antigen (CEA) is an intercellular adhesion molecule that plays a major role in colon tumorigenesis. We have identified a novel protein on human monocytes that binds to CEA. A function of monocytes in the processing of CEA is thus implicated. Monocytes migrate from the bloodstream into loose connective tissue and transform into monocyte-macrophages. Monocytes are seen present in the area of growing tumors but their role(s) in tumorigenesis relative to the expression of CEA-binding protein is not defined. We hypothesize that one of the major factors regulating colorectal carcinoma development is the ability of CEA-producing tumors to activate monocyte-macrophages, via the CEA-binding monocyte protein, to produce cytokines which then promote tumor growth, modulate expression of adhesion molecules on endothelium, and increase tumor cell retention. Thus, a link between CEA-binding protein expression on monocytes and the development of colon cancer is implicated. We propose to characterize the CEA-binding monocyte protein and clone the gene to determine its functional significance in colon tumor development. We have three specific aims. Fist, the monocyte protein will be purified, biochemically characterized and amino acid sequenced to understand its form and nature. The binding domains of CEA and the monocyte protein will be identified to understand its function. An antibody to the monocyte protein will be developed for cloning and functional studies. The gene encoding the novel CEA-binding monocyte protein will be cloned and sequenced to search for homologies with other proteins to determine its functional significance. Second, the expression of cytokines IL1-beta, TNF-alpha and IL-6 by the monocytes in response to CEA binding will be examined by ELISA and by Northern blotting for the detection of cytokine mRNA transcripts. The expression of cytokines will be evaluated in terms of modulation of adhesion molecules to determine their role in tumor cell adhesion. Third, the role(s) of the monocyte protein in colon tumorigenesis will be defined by examining the profile of CEA-binding protein and cytokines (IL-1beta, IL-6 and TNF-alpha) expression of by monocyte in CEA producing and CEA-nonproducing human tumors using quantitative chromogenic assays. We will then examine the relationship between time course of cytokine expression and tumor progression in nude mouse tumor models using CEA producing cells. The broad, long-term goal is to determine the role of the CEA-binding monocyte protein in colon tumorigenesis. An understanding of the mechanisms of colon tumorigenesis relative to expression of the monocyte protein is needed for effective management and ultimately for development of therapeutic approaches to control and prevent this disease.